This invention relates to means for limiting rotation of a member about its axis, and particularly the invention is concerned with a device for limiting the maximum number of rotational turns a crane boom is permitted to make about its vertical axis.
Many types of cranes, and similar devices, are required to rotate through more than 360.degree.. This requirement introduces problems in that wrenches carried by the cranes must be supplied by a source of motive force, such as by electrical conductors or hydraulic lines. If rotatable cranes are permitted to be rotated without limitation, such conductors or lines can eventually be twisted until they are damaged or destroyed. If a crane is limited to not more than 360.degree. of rotation, it is easy to limit the maximum angular rotation. However, it is frequently desirable to be able to rotate a crane more than 360.degree., and in fact, to be able to rotate it for several turns in either direction. At the same time, the maximum number of turns must be limited as above indicated to prevent damage or destruction to conductors or lines.
While the rotation limiter apparatus is particularly adaptable for use on cranes and will be described as applied to this environment for purposes of exemplification, the invention is not in any sense limited to use with cranes, but may be employed where an inexpensive device is needed to limit rotation of one object about an axis relative to another.